Nervous System and Special Senses PDF

Nervous System Functions of the Nervous System ∙ Sensory input – gathering information ∙ To monitor changes occurring inside and outside the body ∙ Stimuli ∙ Integration ∙ To process and interpret sensory input and decide if action is needed Functions of the Nervous System ∙ Motor...

Nervous System Functions of the Nervous System ∙ Sensory input – gathering information ∙ To monitor changes occurring inside and outside the body ∙ Stimuli ∙ Integration ∙ To process and interpret sensory input and decide if action is needed Functions of the Nervous System ∙ Motor output ∙ A response to integrated stimuli ∙ The response activates muscles or glands Structural Classification of the Nervous System ∙ Central nervous system (CNS) ∙ Brain ∙ Spinal cord ∙ Peripheral nervous system (PNS) ∙ Nerve outside the brain and spinal cord Functional Classification of the Peripheral Nervous System ∙ Sensory (afferent) division ∙ Nerve fibers that carry information to the central nervous system Functional Classification of the Peripheral Nervous System ∙ Motor (efferent) division ∙ Nerve fibers that carry impulses away from the central nervous system Functional Classification of the Peripheral Nervous System ∙ Motor (efferent) division ∙ Two subdivisions ∙ Somatic nervous system = voluntary ∙ Autonomic nervous system = involuntary Nervous Tissue: Support Cells (Neuroglia) ∙ Astrocytes ∙ Abundant, star-shaped cells ∙ Brace neurons ∙ Form barrier between capillaries and neurons ∙ Control the chemical environment of the brain Nervous Tissue: Support Cells ∙ Microglia ∙ Spider-like phagocytes ∙ Dispose of debris ∙ Ependymal cells ∙ Line cavities of the brain and spinal cord ∙ Circulate cerebrospinal fluid Nervous Tissue: Support Cells ∙ Oligodendrocytes ∙ Produce myelin sheath around nerve fibers in the central nervous system Nervous Tissue: Support Cells ∙ Satellite cells ∙ Protect neuron cell bodies ∙ Schwann cells ∙ Form myelin sheath in the peripheral nervous system Nervous Tissue: Neurons ∙ Neurons = nerve cells ∙ Cells specialized to transmit messages ∙ Major regions of neurons ∙ Cell body – nucleus and metabolic center of the cell ∙ Processes – fibers that extend from the cell body Neuron Anatomy ∙ Cell body ∙ Nissl substance – specialized rough endoplasmic reticulum ∙ Neurofibrils – intermediate cytoskeleton that maintains cell shape Neuron Anatomy ∙ Cell body ∙ Nucleus ∙ Large nucleolus Neuron Anatomy ∙ Extensions outside the cell body ∙ Dendrites – conduct impulses toward the cell body ∙ Axons – conduct impulses away from the cell body Axons and Nerve Impulses ∙ Axons end in axonal terminals ∙ Axonal terminals contain vesicles with neurotransmitters ∙ Axonal terminals are separated from the next neuron by a gap ∙ Synaptic cleft – gap between adjacent neurons Nerve Fiber Coverings ∙ Schwann cells – produce myelin sheaths in jelly-roll like fashion ∙ Nodes of Ranvier – gaps in myelin sheath along the axon Functional Classification of Neurons ∙ Sensory (afferent) neurons ∙ Carry impulses from the sensory receptors ∙ Cutaneous sense organs ∙ Proprioceptors – detect stretch or tension ∙ Motor (efferent) neurons ∙ Carry impulses from the central nervous system Functional Classification of Neurons ∙ Interneurons (association neurons) ∙ Found in neural pathways in the central nervous system ∙ Connect sensory and motor neurons Neuron Classification Structural Classification of Neurons ∙ Multipolar neurons – many extensions from the cell body Structural Classification of Neurons ∙ Bipolar neurons – one axon and one dendrite Structural Classification of Neurons ∙ Unipolar neurons – have a short single process leaving the cell body Functional Properties of Neurons ∙ Irritability – ability to respond to stimuli ∙ Conductivity – ability to transmit an impulse ∙ The plasma membrane at rest is polarized ∙ Fewer positive ions are inside the cell than outside the cell Starting a Nerve Impulse ∙ Depolarization – a stimulus depolarizes the neuron’s membrane ∙ A deploarized membrane allows sodium (Na+) to flow inside the membrane ∙ The exchange of ions initiates an action potential in the neuron The Action Potential ∙ If the action potential (nerve impulse) starts, it is propagated over the entire axon ∙ Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane ∙ The sodium-potassium pump restores the original configuration ∙ This action requires ATP Nerve Impulse Propagation ∙ The impulse continues to move toward the cell body ∙ Impulses travel faster when fibers have a myelin sheath Continuation of the Nerve Impulse between Neurons ∙ Impulses are able to cross the synapse to another nerve ∙ Neurotransmitter is released from a nerve’s axon terminal The Reflex Arc ∙ Reflex – rapid, predictable, and involuntary responses to stimuli ∙ Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector Simple Reflex Arc Types of Reflexes and Regulation ∙ Autonomic reflexes ∙ Smooth muscle regulation ∙ Heart and blood pressure regulation ∙ Regulation of glands ∙ Digestive system regulation ∙ Somatic reflexes ∙ Activation of skeletal muscles Central Nervous System (CNS) ∙ CNS develops from the embryonic neural tube ∙ The neural tube becomes the brain and spinal cord ∙ The opening of the neural tube becomes the ventricles Regions of the Brain ∙ Cerebral hemispheres ∙ Diencephalon ∙ Brain stem ∙ Cerebellum Cerebral Hemispheres (Cerebrum) ∙ Paired (left and right) superior parts of the brain ∙ Include more than half of the brain mass Cerebral Hemispheres (Cerebrum) ∙ The surface is made of ridges (gyri) and grooves (sulci) Lobes of the Cerebrum ∙ Fissures (deep grooves) divide the cerebrum into lobes ∙ Surface lobes of the cerebrum ∙ Frontal lobe ∙ Parietal lobe ∙ Occipital lobe ∙ Temporal lobe Specialized Areas of the Cerebrum ∙ Somatic sensory area – receives impulses from the body’s sensory receptors ∙ Primary motor area – sends impulses to skeletal muscles ∙ Broca’s area – involved in our ability to speak Specialized Area of the Cerebrum ∙ Interpretation areas of the cerebrum ∙ Speech/language region ∙ Language comprehension region ∙ General interpretation area Specialized Area of the Cerebrum Layers of the Cerebrum ∙ Gray matter ∙ Outer layer ∙ Composed mostly of neuron cell bodies ∙ White matter Layers of the Cerebrum ∙ Basal nuclei – internal islands of gray matter Diencephalon ∙ Sits on top of the brain stem ∙ Enclosed by the cerebral hemispheres ∙ Made of three parts ∙ Thalamus ∙ Hypothalamus ∙ Epithalamus Thalamus ∙ Surrounds the third ventricle ∙ The relay station for sensory impulses ∙ Transfers impulses to the correct part of the cortex for localization and interpretation Hypothalamus ∙ Under the thalamus ∙ Important autonomic nervous system center ∙ Helps regulate body temperature ∙ Controls water balance ∙ Regulates metabolism Hypothalamus ∙ An important part of the limbic system (emotions) ∙ The pituitary gland is attached to the hypothalamus Epithalamus ∙ Forms the roof of the third ventricle ∙ Houses the pineal body (an endocrine gland) ∙ Includes the choroid plexus – forms cerebrospinal fluid Brain Stem ∙ Attaches to the spinal cord ∙ Parts of the brain stem ∙ Midbrain ∙ Pons ∙ Medulla oblongata Brain Stem Midbrain ∙ Mostly composed of tracts of nerve fibers ∙ Has two bulging fiber tracts – cerebral peduncles ∙ Has four rounded protrusions – corpora quadrigemina ∙ Reflex centers for vision and hearing Pons ∙ The bulging center part of the brain stem ∙ Mostly composed of fiber tracts ∙ Includes nuclei involved in the control of breathing Medulla Oblongata ∙ The lowest part of the brain stem ∙ Merges into the spinal cord ∙ Includes important fiber tracts ∙ Contains important control centers ∙ Heart rate control ∙ Blood pressure regulation ∙ Breathing ∙ Swallowing ∙ Vomiting Reticular Formation ∙ Diffuse mass of gray matter along the brain stem ∙ Involved in motor control of visceral organs ∙ Reticular activating system plays a role in awake/sleep cycles and consciousness Cerebellum ∙ Two hemispheres with convoluted surfaces ∙ Provides involuntary coordination of body movements Cerebellum Protection of the Central Nervous System ∙ Scalp and skin ∙ Skull and vertebral column ∙ Meninges Protection of the Central Nervous System ∙ Cerebrospinal fluid ∙ Blood brain barrier Meninges ∙ Dura mater ∙ Double-layered external covering ∙ Periosteum – attached to surface of the skull ∙ Meningeal layer – outer covering of the brain ∙ Folds inward in several areas Meninges ∙ Arachnoid layer ∙ Middle layer ∙ Web-like ∙ Pia mater ∙ Internal layer ∙ Clings to the surface of the brain Cerebrospinal Fluid ∙ Similar to blood plasma composition ∙ Formed by the choroid plexus ∙ Forms a watery cushion to protect the brain ∙ Circulated in arachnoid space, ventricles, and central canal of the spinal cord Ventricles and Location of the Cerebrospinal Fluid Blood Brain Barrier ∙ Includes the least permeable capillaries of the body ∙ Excludes many potentially harmful substances ∙ Useless against some substances ∙ Respiratory gases ∙ Alcohol ∙ Nicotine ∙ Anesthesia Spinal Cord ∙ Extends from the medulla oblongata to the region of T12 ∙ Below T12 is the cauda equina (a collection of spinal nerves) Spinal Cord Anatomy ∙ Internal gray matter - mostly cell bodies ∙ Dorsal (posterior) horns ∙ Anterior (ventral) horns Spinal Cord Anatomy ∙ Central canal filled with cerebrospinal fluid Spinal Cord Anatomy ∙ Meninges cover the spinal cord ∙ Nerves leave at the level of each vertebrae Peripheral Nervous System ∙ Nerves outside the central nervous system ∙ Nerve = bundle of neuron fibers ∙ Neuron fibers are bundled by connective tissue Structure of a Nerve ∙ Endoneurium surrounds each fiber ∙ Groups of fibers are bound into fascicles by perineurium ∙ Fascicles are bound together by epineurium Classification of Nerves ∙ Afferent (sensory) nerves – carry impulses toward the CNS ∙ Efferent (motor) nerves – carry impulses away from the CNS Cranial Nerves ∙ 12 pairs of nerves that mostly serve the head and neck ∙ Numbered in order, front to back ∙ Most are mixed nerves, but three are sensory only Cranial Nerves ∙ I Olfactory nerve – sensory for smell ∙ II Optic nerve – sensory for vision ∙ III Oculomotor nerve – motor fibers to eye muscles ∙ IV Trochlear – motor fiber to eye muscles Cranial Nerves ∙ V Trigeminal nerve – sensory for the face; motor fibers to chewing muscles ∙ VI Abducens nerve – motor fibers to eye muscles ∙ VII Facial nerve – sensory for taste; motor fibers to the face ∙ VIII Vestibulocochlear nerve – sensory for balance and hearing Cranial Nerves ∙ IX Glossopharyngeal nerve – sensory for taste; motor fibers to the pharynx ∙ X Vagus nerves – sensory and motor fibers for pharynx, larynx, and viscera ∙ XI Accessory nerve – motor fibers to neck and upper back ∙ XII Hypoglossal nerve – motor fibers to tongue Spinal Nerves ∙ There is a pair of spinal nerves at the level of each vertebrae for a total of 31 pairs ∙ Spinal nerves are formed by the combination of the ventral and dorsal roots of the spinal cord ∙ Spinal nerves are named for the region from which they arise Anatomy of Spinal Nerves ∙ Spinal nerves divide soon after leaving the spinal cord ∙ Dorsal rami – serve the skin and muscles of the posterior trunk ∙ Ventral rami – forms a complex of networks (plexus) for the anterior Examples of Nerve Distribution Autonomic Nervous System ∙ The involuntary branch of the nervous system ∙ Consists of only motor nerves ∙ Divided into two divisions ∙ Sympathetic division ∙ Parasympathetic division Differences Between Somatic and Autonomic Nervous Systems ∙ Nerves ∙ Somatic – one motor neuron ∙ Autonomic – preganglionic and postganglionic nerves ∙ Effector organs ∙ Somatic – skeletal muscle ∙ Autonomic – smooth muscle, cardiac muscle,and glands Differences Between Somatic and Autonomic Nervous Systems ∙ Neurotransmitters ∙ Somatic – always use acetylcholine ∙ Autonomic – use acetylcholine, epinephrin e, or norepinephrine Autonomic Functioning ∙ Sympathetic – “fight-or-flight” ∙ Response to unusual stimulus ∙ Takes over to increase activities ∙ Remember as the “E” division = exercise, excitement, emergency, and embarrassment Autonomic Functioning ∙ Parasympathetic – housekeeping activites ∙ Conserves energy ∙ Maintains daily necessary body functions ∙ Remember as the “D” division - digestion, defecation, and diuresis SPECIAL SENSES The Senses ∙ General senses of touch ∙ Temperature ∙ Pressure ∙ Pain ∙ Special senses ∙ Smell ∙ Taste ∙ Sight ∙ Hearing ∙ Equilibrium The Eye and Vision ∙ 70 percent of all sensory receptors are in the eyes ∙ Each eye has over a million nerve fibers ∙ Protection for the eye ∙ Most of the eye is enclosed in a bony orbit ∙ A cushion of fat surrounds most of the eye Accessory Structures of the Eye ∙ Eyelids ∙ Eyelashes Accessory Structures of the Eye ∙ Meibomian glands – modified sebacious glands produce an oily secretion to lubricate the eye Accessory Structures of the Eye ∙ Conjunctiva ∙ Membrane that lines the eyelids ∙ Connects to the surface of the eye ∙ Secretes mucus to lubricate the eye Accessory Structures of the Eye ∙ Ciliary glands – modified sweat glands between the eyelashes Accessory Structures of the Eye ∙ Lacrimal apparatus ∙ Lacrimal gland – produces lacrimal fluid ∙ Lacrimal canals – drains lacrimal fluid from eyes Accessory Structures of the Eye ∙ Lacrimal sac – provides passage of lacrimal fluid towards nasal cavity Accessory Structures of the Eye ∙ Nasolacrimal duct – empties lacrimal fluid into the nasal cavity Function of the Lacrimal Apparatus ∙ Properties of lacrimal fluid ∙ Dilute salt solution (tears) ∙ Contains antibodies and lysozyme ∙ Protects, moistens, and lubricates the eye ∙ Empties into the nasal cavity Extrinsic Eye Muscles ∙ Muscles attach to the outer surface of the eye ∙ Produce eye movements Structure of the Eye ∙ The wall is composed of three tunics ∙ Fibrous tunic – outside layer ∙ Choroid – middle layer ∙ Sensory tunic – inside layer The Fibrous Tunic ∙ Sclera ∙ White connective tissue layer ∙ Seen anteriorly as the “white of the eye” ∙ Cornea ∙ Transparent, central anterior portion ∙ Allows for light to pass through ∙ Repairs itself easily Choroid Layer ∙ Blood-rich nutritive tunic ∙ Pigment prevents light from scattering ∙ Modified interiorly into two structures ∙ Cilliary body – smooth muscle ∙ Iris ∙ Pigmented layer that gives eye color ∙ Pupil – rounded opening in the iris Sensory Tunic (Retina) ∙ Contains receptor cells (photoreceptors) ∙ Rods ∙ Cones ∙ Signals pass from photoreceptors via a two-neuron chain ∙ Bipolar neurons ∙ Ganglion cells ∙ Signals leave the retina toward the brain through the optic nerve Neurons of the Retina Neurons of the Retina and Vision ∙ Rods ∙ Most are found towards the edges of the retina ∙ Allow dim light vision and peripheral vision ∙ Perception is all in gray tones Neurons of the Retina and Vision ∙ Cones ∙ Allow for detailed color vision ∙ Densest in the center of the retina ∙ Fovea centralis – area of the retina with only cones ∙ No photoreceptor cells are at the optic disk, or blind spot Cone Sensitivity ∙ There are three types of cones ∙ Different cones are sensitive to different wavelengths ∙ Color blindness is the result of lack of one cone type Lens ∙ Biconvex crystal-like structure ∙ Held in place by a suspensory ligament attached to the ciliary body Internal Eye Chamber Fluids ∙ Aqueous humor ∙ Watery fluid found in chamber between the lens and cornea ∙ Similar to blood plasma ∙ Helps maintain intraocular pressure ∙ Provides nutrients for the lens and cornea ∙ Reabsorbed into venous blood through the canal of Schlemm Internal Eye Chamber Fluids ∙ Vitreous humor ∙ Gel-like substance behind the lens ∙ Keeps the eye from collapsing ∙ Lasts a lifetime and is not replaced Lens Accommodation ∙ Light must be focused to a point on the retina for optimal vision ∙ The eye is set for distance vision (over 20 ft away) ∙ The lens must change shape to focus for closer objects Images Formed on the Retina Visual Pathway ∙ Visual pathways conduct impulses from the retina from the visual cortex of the occipital lobe and are perceived as vision Eye Reflexes ∙ Internal muscles are controlled by the autonomic nervous system ∙ Bright light causes pupils to constrict through action of radial and ciliary muscles ∙ Viewing close objects causes accommodation ∙ External muscles control eye movement to follow objects ∙ Viewing close objects causes convergence (eyes moving medially) The Ear ∙ Houses two senses ∙ Hearing ∙ Equilibrium (balance) ∙ Receptors are mechanoreceptors ∙ Different organs house receptors for each sense Anatomy of the Ear ∙ The ear is divided into three areas ∙ Outer (external) ear ∙ Middle ear ∙ Inner ear The External Ear ∙ Involved in hearing only ∙ Structures of the external ear ∙ Pinna (auricle) ∙ External auditory canal The External Auditory Canal ∙ Narrow chamber in the temporal bone ∙ Lined with skin ∙ Ceruminous (wax) glands are present ∙ Ends at the tympanic membrane The Middle Ear or Tympanic Cavity ∙ Air-filled cavity within the temporal bone ∙ Only involved in the sense of hearing The Middle Ear or Tympanic Cavity ∙ Two tubes are associated with the inner ear ∙ The opening from the auditory canal is covered by the tympanic membrane ∙ The auditory tube connecting the middle ear with the nasopharynx ∙ Allows for equalizing pressure during yawning or swallowing Bones of the Tympanic Cavity ∙ Three bones span the cavity ∙ Malleus (hammer) ∙ Incus (anvil) ∙ Stapes (stirrup) Bones of the Tympanic Cavity ∙ Vibrations from eardrum move the malleus ∙ These bones transfer sound to the inner ear Inner Ear or Bony Labyrinth ∙ Includes sense organs for hearing and balance Inner Ear or Bony Labrynth ∙ A maze of bony chambers within the temporal bone ∙ Cochlea ∙ Vestibule ∙ Semicircular canals Organs of Hearing ∙ Organ of Corti ∙ Located within the cochlea ∙ Receptors = hair cells on the basilar membrane ∙ Gel-like tectorial membrane is capable of bending hair cells ∙ Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe Organs of Hearing Mechanisms of Hearing ∙ Vibrations from sound waves move tectorial membrane ∙ Hair cells are bent by the membrane ∙ An action potential starts in the cochlear nerve ∙ Continued stimulation can lead to adaptation Organs of Equilibrium ∙ Receptor cells are in two structures ∙ Vestibule ∙ Semicircular canals ∙ Equilibrium has two functional parts ∙ Static equilibrium ∙ Dynamic equilibrium Static Equilibrium ∙ Maculae – receptors in the vestibule ∙ Report on the position of the head ∙ Send information via the vestibular nerve ∙ Anatomy of the maculae ∙ Hair cells are embedded in the otolithic membrane ∙ Otoliths (tiny stones) float in a gel around the hair cells ∙ Movements cause otoliths to bend the hair cells Function of Maculae Dynamic Equilibrium ∙ Crista ampullaris – receptors in the semicircular canals ∙ Tuft of hair cells ∙ Cupula (gelatinous cap) covers the hair cells Dynamic Equilibrium ∙ Action of angular head movements ∙ The cupula stimulates the hair cells ∙ An impulse is sent via the vestibular nerve to the cerebellum Chemical Senses – Taste and Smell ∙ Both senses use chemoreceptors ∙ Stimulated by chemicals in solution ∙ Taste has four types of receptors ∙ Smell can differentiate a large range of chemicals ∙ Both senses complement each other and respond to many of the same stimuli Olfaction – The Sense of Smell ∙ Olfactory receptors are in the roof of the nasal cavity ∙ Neurons with long cilia ∙ Impulses are transmitted via the olfactory nerve Olfactory Epithelium The Sense of Taste ∙ Taste buds house the receptor organs ∙ Location of taste buds ∙ Most are on the tongue ∙ Soft palate ∙ Cheeks Structure of Taste Buds ∙ Gustatory cells are the receptors ∙ Have gustatory hairs (long microvilli) ∙ Hairs are stimulated by chemicals dissolved in saliva Structure of Taste Buds ∙ Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas ∙ Facial nerve ∙ Glossopharyngeal nerve ∙ Vagus nerve Taste Sensations ∙ Sweet receptors ∙ Sour receptors ∙ Bitter receptors ∙ Salty receptors